[rustdoc] --static-root-path is ignored for proc macro crates if --target is also passed

[jyn514]

I've been on a wild ride trying to figure out exactly what's been going on.

Minimal example: clone https://github.com/la10736/rstest and run RUSTDOCFLAGS="-Z unstable-options --static-root-path /" cargo +nightly doc --target x86_64-unknown-linux-gnu. The links to static files should start with /; instead they start with ../.

Note that if you omit --target, the --static-root-path / argument works fine. I'm not sure why they conflict in this way.

This is the root cause of rust-lang/docs.rs#422.
This is similar but not the same as #62940.

cc @QuietMisdreavus @pietroalbini

[QuietMisdreavus]

This is a Cargo bug, which is easier to demonstrate not directly on rstest, but on an empty crate which depends on it:

$ RUSTDOCFLAGS="-Z unstable-options --static-root-path /" cargo +nightly doc --target x86_64-pc-windows-gnu --verbose
(...cutting out other crate builds...)
 Documenting rstest v0.4.1
     Running `rustdoc --edition=2018 --crate-type proc-macro --crate-name rstest /home/misdreavus/.cargo/registry/src/git.godevs.top-1ecc6299db9ec823/rstest-0.4.1/src/lib.rs --cap-lints allow -o /home/misdreavus/git/asdf/target/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/home/misdreavus/git/asdf/target/debug/deps --extern cfg_if=/home/misdreavus/git/asdf/target/debug/deps/libcfg_if-e81fd561ea5d778d.rmeta --extern itertools=/home/misdreavus/git/asdf/target/debug/deps/libitertools-fc795270e0118033.rmeta --extern proc_macro2=/home/misdreavus/git/asdf/target/debug/deps/libproc_macro2-28ac7b73e9431dcd.rmeta --extern quote=/home/misdreavus/git/asdf/target/debug/deps/libquote-c3d8fb0ee445b121.rmeta --extern syn=/home/misdreavus/git/asdf/target/debug/deps/libsyn-3cb4f46f3856d11c.rmeta --cfg use_proc_macro_diagnostic`
 Documenting asdf v0.1.0 (/home/misdreavus/git/asdf)
     Running `rustdoc --edition=2018 --crate-type lib --crate-name asdf src/lib.rs --target x86_64-pc-windows-gnu -o /home/misdreavus/git/asdf/target/x86_64-pc-windows-gnu/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/home/misdreavus/git/asdf/target/x86_64-pc-windows-gnu/debug/deps -L dependency=/home/misdreavus/git/asdf/target/debug/deps --extern qwop=/home/misdreavus/git/asdf/target/x86_64-pc-windows-gnu/debug/deps/libqwop-00f1cec7bc7f8935.rmeta --extern rstest=/home/misdreavus/git/asdf/target/debug/deps/librstest-4735249459e3b68f.so -Z unstable-options --static-root-path /`
    Finished dev [unoptimized + debuginfo] target(s) in 21.89s

Compare the commands given for rstest versus the leaf crate asdf. rstest is given a -o argument of /home/misdreavus/git/asdf/target/doc, whereas asdf is given /home/misdreavus/git/asdf/target/x86_64-pc-windows-gnu/doc. rstest is also not given RUSTDOCFLAGS, which is why --static-root-path is being ignored - it's not being given at all.

This effect is more pronounced when the leaf crate is itself a proc-macro crate; there, all the docs go into target/doc instead of target/$target/doc, and no crate gets RUSTDOCFLAGS. For example, if i run the same command directly in rstest:

$ RUSTDOCFLAGS="-Z unstable-options --static-root-path /" cargo +nightly doc --target x86_64-pc-windows-gnu --verbose
(...cutting out other crate builds...)
 Documenting syn v1.0.5
     Running `rustdoc --edition=2018 --crate-type lib --crate-name syn /home/misdreavus/.cargo/registry/src/git.godevs.top-1ecc6299db9ec823/syn-1.0.5/src/lib.rs --cap-lints allow -o /home/misdreavus/clones/rstest/target/doc --cfg 'feature="clone-impls"' --cfg 'feature="default"' --cfg 'feature="derive"' --cfg 'feature="extra-traits"' --cfg 'feature="full"' --cfg 'feature="parsing"' --cfg 'feature="printing"' --cfg 'feature="proc-macro"' --cfg 'feature="quote"' --cfg 'feature="visit"' --error-format=json --json=diagnostic-rendered-ansi -L dependency=/home/misdreavus/clones/rstest/target/debug/deps --extern proc_macro2=/home/misdreavus/clones/rstest/target/debug/deps/libproc_macro2-28ac7b73e9431dcd.rmeta --extern quote=/home/misdreavus/clones/rstest/target/debug/deps/libquote-c3d8fb0ee445b121.rmeta --extern unicode_xid=/home/misdreavus/clones/rstest/target/debug/deps/libunicode_xid-87ca1b5df9f4f475.rmeta`
 Documenting rstest v0.4.0 (/home/misdreavus/clones/rstest)
     Running `rustdoc --edition=2018 --crate-type proc-macro --crate-name rstest src/lib.rs -o /home/misdreavus/clones/rstest/target/doc --error-format=json --json=diagnostic-rendered-ansi -L dependency=/home/misdreavus/clones/rstest/target/debug/deps --extern cfg_if=/home/misdreavus/clones/rstest/target/debug/deps/libcfg_if-e81fd561ea5d778d.rmeta --extern itertools=/home/misdreavus/clones/rstest/target/debug/deps/libitertools-6b909a299a131f9f.rmeta --extern proc_macro2=/home/misdreavus/clones/rstest/target/debug/deps/libproc_macro2-28ac7b73e9431dcd.rmeta --extern quote=/home/misdreavus/clones/rstest/target/debug/deps/libquote-c3d8fb0ee445b121.rmeta --extern syn=/home/misdreavus/clones/rstest/target/debug/deps/libsyn-c9363dee89805d6e.rmeta --cfg use_proc_macro_diagnostic`
    Finished dev [unoptimized + debuginfo] target(s) in 11.01s

Note here that neither syn nor rstest get the correct -o directory, nor do they get RUSTDOCFLAGS.

[jyn514]

rstest is also not given RUSTDOCFLAGS, which is why --static-root-path is being ignored - it's not being given at all.

Looks like this is rust-lang/cargo#4423.

[QuietMisdreavus]

rstest is also not given RUSTDOCFLAGS, which is why --static-root-path is being ignored - it's not being given at all.

Looks like this is rust-lang/cargo#4423.

That seems to be about build scripts, though - does it apply to proc-macros as well?

[jyn514]

I think so, see rust-lang/cargo#4423 (comment) and rust-lang/cargo#4423 (comment)

[Mark-Simulacrum]

I believe this is a Cargo bug, not a bug in rustdoc, so closing (the option just isn't passed).